Solvent dewaxing process



April 21, 1942. o. s'. POKORNY SOLVENT DEWAXING PROCESS Filed Nov. 19',1938 wax , waxy constituents from the oil. It is alsoknown it is knownthat the rate at. which the jchille talline structure secured. It isalsotknownthat Patented Apr. 21, 1942 UNIT soLvEnT Emma PROCESS IOlidrich S. ifiikt rm;. samag Ontario. Canada, as-

The present invention relates to the dewaxing of petroleum oils. Theinvention is particularly p directed to an improvedprocessofprecipitating waxy constituents, from the oil; The inyentienespecially relates to a process in. whichaa waxy 15 distillate isblended with a suitable 'dewaxing solvent, the mixture heated to--secure complete miscibility of the oil, the waxy-constituents andsolvent, and then shoclr or rapidly chilled;through an initial coolingstage slow ly chilled through an intermediate, stage and. then; rapidlychilled through the final stage. a 1 a It is well known in the art todewax waxy petroleum oils by various procedurea; usual process isto takea relatively wide waxy distillate out containing lighter boilinghydrocarbons and to chill to a temperature at which thewaxy constituentsprecipitate. The lighter--boi1ing1hy 1 drocarbons serve as diluents andfacilitate sub".- sequent filteringfof the precipitatedwaxy constituents- 1 The precipitated waxy constituents l I may, also beseparated by sedimentation, centrifuging andfthe like. Anotherprocedureis to use dewaxing solvents or,solvent riiixti jres of the class whichhave afpreferential selectivity for non-waxy constituents or tendtc)precipitate the to add other substances such as 'dewaxing and w vfiltering aids and the like.

a The waxy distillate is chilled inany suitable manner in order to lowerthe temperature to a point at which the waxy constitue ts pr wing thisprocedure the Waxy constitums" are separated from the dewaxed oil bysediment tion, filteringor other means. In these processes mixture maybesubsequently filtered is a func tion, to a large extent, of the typeof wax crysa desirable wax crystalline structure. will; be se- I curedif the rate of chilling is.controlledzso that' the temperature islowered" at a, -.relativ ely low rate. -By operating in this manner, fltering rates can be materially increased and the capacity of thefiltering equipment substantially liner-eased.

This process, however, is not;.entirely" satisfactory since in order tosecure i i-desirable wax crystalline structure; the timenecessary'toucool from the miscibility temperature; to the dewaxingtemperature is unduly 10ng. This =factoris of a criticalnaturewhenit-ismonsidered that in order to successfully operateacommercial process it is necessary that the maximum-capacity of theequipment .be secured. Thus; fQIiQGX- ample, if the cooling. time' bedoubled. the: cacc signor to Standard .Oil Development Company, acorporationoiipelaware I .pacity of the equipment would be halved which.would materially increase the investment necessary and depreciationcharges of the-operation. ljv have now discovered a process by which itis possible to chill a waxy distillate in a minimum of, time andtosecu'rea wax crystalline structure which will give subsequent maximumfiltering rates. Thus, by my process overall efiiciency ofthe chillersand the filters is secured. Ihave discovered that a critical rangeexists in the wax crystallization "curve insofar as the waxcrystallization structure affects subsequent; filtering rates. in Viewof this discovery 1 regulatemy process to secureoptimum crystallinestructure over the critical rangeand after passing through this range Ioperate in a manner to secure the maximum cooling rate. I have foundthat the filtering ratesgare almost a direct function of the characterof the crystalline structure of the. relatively h igh IneltingupointWaxes and that the waxq zystalline structuresof the relatively lowmelting point waxes do not adversely affect the filtering rates eitherwhen chilled slowly or rapidly. As the temperature of the solutiondrops, the relatively high melting point waxes are precipitated. As thetemperature is further lowered,

, progressively lower melting point waxes are precipitated. Thewaxesthat precipitate out at a temperature lot about +35 F; and lowerapparently do not form deleterious crystalline structures which willaffect the filtering rate, butthe crystalsforrned in the range fromabout 35 j to+9 5 Fillwillladversely ailect the rate,

provided careis 'not used to secure the desired crystalline structure aa Mypme s maybe readily understood by ref-' ...erence to the attacheddiagrammatical flow plan showing one modification of the invention.

Waxy distillate is introduced into chiller I by 407 meansof feed linei.Asuitable dewaxing solvent .ismixed with the Waxy distillate andintroducedinto feed line {by means of line 3. The

' .waxydistillate is usually heated in heater. 5yto aytemperature atwhich complete miscibility occurs between the oil, the waxy constituentsand the; dewaxing solvent. The diluted waxy distillate is then passed tochiller I where the temperature is lowered through an initial stageeither by direct or indirect cooling. For example, if ;the dewaxingsolvent comprises propane, sufficient propane is allowed to evaporate tosecure rapid chilling through this range. The propane is removed bymeans ofgline 6. The partially chilled mixtureis-removed from the.chiller I by; means of line I and introduced into chiller The dewaxedoil and solvent are: removed by means of line l and the wax cake bymeans of line I6.

The process of the present invention may be varied widely. It is to beunderstood that any suitable solvent, as for example, ketones,chlorinated hydrocarbons, higher esters of acetic acid,- various mixedsolvents such as benzol-methyl ethyl ketone, carbontetrachloride-ethylene dichloride, and the like may be employed.Although the present invention is particularly adapted for use insolvent dewaxing operations, itmay be utilized in the dewaxing ofrelatively wide cut distillates employing no dewaxing solvents. Thefiltering operation may be conducted in one or more stages. It is alsowithin the scope of the present invention to employ solvent washing fordiluting the incoming'waxy stock charge, as for example in thosedewaxing processes where all the fresh solvent required in the processis used first as wash solvent and the wash solution is collectedseparately and recycled to the incoming waxy charge for dilution massfrom the complete miscibility temperature of about 150 F. to about 90 F.in less than one minute by means of flash cooling. In general, the massshould be chilled from the complete miscibility temperature to about 90F. in less than about three minutes. The rate of chilling in theintermediate stage should be less than about 3 per minute, preferablynot over 2 per minute. The chilling in the final stage, as in theinitial stage, may be conducted to secure as rapid 'a rate aseconomically desirable. Desirable results are secured when the chillingin the range from about 150 F. to 90 F. is of the order of per minuteand when the chilling rate in the range from about 35 F. to the dewaxingI temperature is in'excess of 5 per minute.

In order to further illustrate the invention. the following example isgiven which should not be construed as limiting the invention in anymanner whatsoever.

Example An intermediate lubricating oil distillate having a viscosity of74 seconds at 210 F. was dewaxed in the following manner. One andonehalf volumes of methyl normal butyl ketone were added to one volumeof oil and the mixture heated to a temperature of 120 F. Variousoperations were conducted, chilling the mixture at different rates overvarious cooling ranges to dewaxing temperatures in the range from 12 to15 F. The solidification points secured on the waxes were in the rangefrom 11 to 13 F. The results of these operations may be summarized asfollows:

TABLE 1 Efiect of the rate of chilling on the dewamed oil throughoutStock: Intermediate motor distillate 74 Say. vise. at 210 F. Solvent:Methyl n-butyl ketone, dilution l.5:l.0, suction 14 inches of mercury.

Capacity, using 0 t field 0g Total Fm t 100%. tbased on pera 1on ewaxeune ermg re 0 presen process No. Cmmng rate 011, perunits forvol./hr./sq. ft.

cent chilling Chillers Filters Controlled chilling 1 F./min 93 108 5.929. 6 115.0 Controlled ch1llmg 3 F./min 91 36 2. 6 88.8 51.0 Shockchillin H 85 2. 2 43. 2

Chilling rate in the temperature range 120-90 F. 9050 F. Bil-35 F. 35-l2F.

4 1 FJrnin. 1 F./min. 3 F./mln 3 F./min. 92 as 4.1 as. s so. 4 5 2F./min. 2 FJm n. 2 F./1nln Shock ch. 91 4. 7 71. 2 92. 2 6 Shock ch. 2F./m1n. 2 F Imm Shock ch. 92 32 5. 1 100. 0 100.0

purposes. The ranges of the respective cooling stages will, of course,depend upon the particular lube distillate being dewaxed, the solvent orsolvent mixture being employed, as well as upon the type of waxyconstituents present. It is to be understood that some overlapping willoccur.

However, in general, the initial cooling stage is 'from the completemiscibility temperature to a regard to the type of wax crystals beingformed. 'For example, it may be desirable to cool the From the abovedata it may be readily seen that when operating in accordance with thepresent process the capacity of the cooling equipment'was increased by300% and the capacity of the filters was decreased by about 13% overcontrolled chilling of 1 per minute over the entire range. The processof the present invention as illustrated by operation No. 6 is a distinctadvantage over the process as illustrated by operations No. 1 to No. 5inclusive. The best other operation was operation No. 2 in which thecapacity of the chilling equipment was increased by about 89% with theresult that the capacity of'the filtering equipment was reduced to aboutone-half.

' The present-invention is not to be restricted in any mannerwhatsoever, but only by the fol I claim": t r t p 1. Processforfrem'ovingww axy "constituents y i from a petroleum oil waxydistillate comprising adding to said distillate about one and one-half"volumes of methyl normal butyl ketone p'er volume of distillate,heating themixture, to. a tem- Q peratureof about 120 rapidly chilling 1the mixture from thistemperature in an initialcooll ring-stage to about90 LR, slowly chilling the mixture in a secondary cooling stage fromabout 90? F, togabout 35 F., rapidlychilling the mixture in a finalIco'oling stage 'fromfabout35? F.

to about 12 Fl, [and then filtering; the chilled mass to removeth'e-waxyconstituents.

h 2. Process in accordance with claim 1 in which the distillate ischilled in said initial stage at f the'rate o f about 20 perminute,-ischilled in said secondary stage at the rateof about 2 per minute and ischilled in said final cooling stage at 'therate of about 5 per minute. i

3. A method for removing waxy constituents from a petroleum oil waxydistillate which comprises adding methyl n-butyl ketone to thedistillate as a dewaxing solvent, heating the mixture to atemperature ofabout 120 F., to obtain substantially complete miscibility of the waxyconstituents and dewaxing solvent in the distillate, rapidly chillingthe mixture from about 120 F. in an initial cooling stage to about 90 F.at a rate of about 20 F. per minute, slowly chilling the mixture in asecondary cooling stage from about 90F. to about 35 F. at aerate ofabout 2 F. per minute, rapidly chilling the mixture in a finall coolingstage from about 35 F. to about 12 F. at a rate of about 5 F. perminute, andthenfiltering the chilled mixture to remove the precipitatedwaxy constituents.

" OLDRICH S. POKORNY.

